Porphyrin-Based All-Small-Molecule Organic Solar Cells With Absorption-Complementary Nonfullerene Acceptor

It is crucial to minimize the absorption overlap between donor and acceptor for high-efficiency all-small-molecule organic solar cells with high current densities. Considering strong absorption of nonfullerene acceptors 2,2.-((2Z,2?Z)-((4,4,9,9-tetrahexyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b.]dithiophene-2,7-diyl)bis(methanylylidene))bis(3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (IDIC) in the ranges of 650-750 nm, two porphyrin unit-based small molecules containing diketopyrrolopyrrole groups (Dipor and Por) are selected as the electron donor materials because of their weak absorption in this region. Porphyrin dimer Dipor displays a broad photon response from 300 to 1000 nm in the films and its absorption deficiency between the Soret and Q-bands could be perfectly compensated by nonfullerene acceptors IDIC, while monomer Por shows partial overlapping absorption to IDIC in ranges of 650-700 nm and its absorption edge locates at similar to 900 nm. The higher compatibility of porphyrin dimer Dipor and IDIC results in a promising power conversion efficiency of 8.3% with a high short-circuit current density (Jsc) of 20.2 mA cm-2, whereas the devices based on Por: IDIC show a lower power conversion efficiency of 6.3%.

Automated summary

This study emphasizes the importance of minimizing the absorption overlap between the donor and acceptor in all-small-molecule organic solar cells for achieving high current densities. By selecting porphyrin unit-based small molecules with absorption ranges different from the nonfullerene acceptor IDIC, it is possible to enhance the power conversion efficiency of the devices.